Shotgun cartridges typically comprise a propellant charge, a wad and a shot load, all of which are contained within a plastic or paper shell reinforced at one end with a metal case head to contain and direct the created propellant gases through the opposite end of the cartridge. The shotgun wad typically comprises a polymer or fabric body that obturates against the barrel during firing to prevent escape of propellant gases around the slug or through the shot. The wad often comprises a forward facing cup portion or wings that contains the shot or slug as the shot travels through the barrel. Upon exiting the barrel, aerodynamic drag on the cup or the flaring of the wings slows the wad separating the wad from the slug or shot and freeing the projectile(s) to travel onto the target alone.
A primary consideration is determining the performance of a shot loaded shotgun cartridge is determining the maximum effective range at which there is sufficient shot density to accurately strike a target. A standard measurement for determining the effective range of the shotgun cartridge is patterning or measuring the percentage of shot that strikes within a 30 inch circle at 40 yards or other predetermined distance. The tightness of the pattern or the percentage of shot that strikes within the circle can be affected the size and shape of the shot, the size of the propellant load and the separation point between the wad and the shot. For the purposes of this disclosure, the separation point is the point during flight in which wad dispenses the shot load from the cup portion.
In particular, the conventional understanding of the effect of the wad on patterning of the shot load is that the longer the wad remains with the shot during flight, the greater the likelihood that the wad will worsen the patterning of the shot load or produce an irregular shot pattern. Wads are typically designed to incur significant aerodynamic drag upon leaving the muzzle through a forward facing cup portion or flaring wings that slow the wad while the shot and slug continues onto the target. The intentionally poor aerodynamic qualities of the wad can cause the wad to tumble or veer off the desired trajectory. The greater the distance of the separation point from the muzzle the more likely that the wad may negatively impact the trajectory of the shot or the slug. As a result, the wad is typically designed to have a separation point as close to the end of the muzzle as possible.
In certain wads, the wad is commonly formed by folding four separate wings together to define the walls of the cup. The wings flare open immediately upon leaving the muzzle to slow the wad and release the load as soon as possible. Similarly, certain shotgun chokes, such as disclosed in U.S. Pat. No. 7,523,581, slow the wad as the wad passes the choke to begin to separate the shot from the load even before the wad exits the muzzle. In both configurations, the wad is rapidly slowed to facilitate a separation point as close to the muzzle of the barrel as possible.
A similar consideration is that different shot patterns and densities are required for different uses. A choke is typically placed at the muzzle of the shotgun to set the rate at which the shot expands to control the resulting shot pattern. Different chokes are used to create different shot patterns. However, because the choke is positioned at the muzzle of the shotgun, a conventional choke may not sufficiently constrict the shot pattern such that the desired shot pattern is obtained. Certain shotgun cartridges, such as disclosed in U.S. Pat. No. 7,243,603, contain a shot container for receiving the shot and placed within the wad. Upon firing, the shot container is released from the wad and travels a distance with the shot retained within the container before dispensing the shot to expand radially. However, the shot container adds an additional feature to the manufacturing of the shotgun cartridges and can also potentially negatively influence the resulting shot pattern. In addition, the container occupies space within the already limited dimensions of the shotgun cartridge that could be otherwise used for the propellant charge or shot load.
The conventional understanding in the art is that the wad is a hindrance to achieving the desired shot patterning. However, the conventional means of controlling the shot pattern are not always sufficient to provide the desired shot pattern.